1. Field of the Invention
The present invention relates to slack adjusters which are devices used with fluid pressure actuated brakes to accommodate the wear of brake shoes and the like so that the length of the brake actuation stroke remains the same as wear takes place.
2. Description of Related Art
Fluid-actuated brakes with slack adjusters are well known in the art as seen, for example, in the following: U.S. Pat. Nos. 4,676,346; 4,895,228; 5,423,401; 5,848,550; 5,937,974; and 6,397,986. Typically, fluid-actuated brakes have a housing enclosing a piston and cylinder. The piston drives a connecting linkage that is generally tubular. Within the tubular linkage is positioned a push rod that can slide within the tubular linkage. Some type of clutching apparatus is positioned between the tubular linkage and the push rod for driving the rod in a brake-actuating direction but permitting the rod to retreat into the tubular linkage. Also associated with the rod is a slack adjuster comprising a movable stop normally clutched relative to the push rod to restrict the retreat of the push rod by engaging a stop face on the tubular linkage or the housing. The stop must be capable of unclutching and moving along the push rod in the direction opposite the brake-actuation direction if the rod moves beyond its prior normal travel due to brake wear. At such time, the stop is moved by engaging a stop face associated with the housing. It must also be possible to manually force the push rod to retreat into the tubular linkage at the time of brake pad replacement. This requires the unclutching of the stop.
Stops are generally of two types. In one type, the push rod has external threads and the stop comprises a nut that turns on the push rod threads. Clutching action is caused by restricting rotation of the nut relative to the rod as shown, for example, in U.S. Pat. Nos. 4,676,346 and 4,895,228.
In the other type, the push rod has threads or teeth and the stop comprises a collet that surrounds the rod and frictionally grips the teeth. The collet is a tube that has an inner diameter that abuts and squeezes the teeth of the push rod. Axial slits in the tube wall allow slight radial expansion of the tube permitting it to ride over the teeth of the push rod. At one end of the collet tube, a ring of enlarged diameter is located. Axial faces on the ring serve as stop faces for engaging stops associated with the housing or tubular linkage. If sufficient axial force is applied, the collet will unclutch and move axially along the push rod. Collet-type stops in slack adjusters are disclosed, for example, in U.S. Pat. Nos. 5,423,401 and 5,937,974. The slack adjuster collets disclosed in these patents have slack adjuster collets with an enlarged ring end positioned axially away from the brake. The squeezing force of the collet on the teeth of the push rod is the same no matter the axial position of the collet relative to the push rod.